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IF 938 MODDE ET AL. ; emerge and enter the water column during peak discharge when floodplain nursery habitats are connected to the river, allowing larvae to drift into nursery habitats (Modde et al. 2001). In addition, postspawning adults also access nutrient rich floodplains following spawning (Modde and Ir- ving 1998). Thus, locality and timing of razorback sucker spawning are critical and related to hydro- logical events linked to specific life history needs. The recovery plan proposed for razorback suck- ers (USFWS 2002) includes instream flow rec- ommendations requiring minimum flows and ma- nipulating the frequency and timing of discharge to increase floodplain connection at the time when larvae are present (Muth et al. 2002), as well as population augmentation (Nesler et al. 2003). The augmentation plan states that 92,500 subadult (>300 mm total length [TL]) razorback suckers will be stocked over a 5-year period, the goal being to establish a population of 7,540 adults (Nesler et al. 2003). If the number of adult spawners, and thus reproduction, are increased, flow recommen- dations will reconnect nursery habitat to the river and allow access to critical habitat by drifting lar- vae, which should thereby increase the probability of their survival and successful recruitment. How- ever, the ability of stocked fish to contribute to reproduction requires that they are able to locate specific spawning sites upstream of nursery hab- itat. Scholz et al. (1996) provided experimental data suggesting both razorback suckers and Col- orado pikeminnows Pytchocheilus lucius imprint to emergence sites before larval drift. If for this or other reasons hatchery fish introduced into the system are not able to find established spawning sites, the benefits of augmentation will be limited and may even adversely affect recovery if hatchery fish compete for resources with wild fish without contributing offspring. The purpose of this study was to examine whether hatchery-reared fish will show similar spatial and temporal use of a spawn- ing area used by wild fish and to examine the po- tential importance of the results to the recovery effort. Methods Study area.-The study area is the primary spawning location for razorback suckers in the middle Green River, Utah, located at approxi- mately river kilometer (rkm) 504 (river course dis- tance upstream of the confluence with the Colo- rado River). This site, referred to as the Escalante (Modde et al. 1996) or Jensen (Tyus and Karp 1990) spawning site, is located along the eastern Cub Creek Uta h ,4! der QL Spawning rkm 505 `Data Logger FIGURE 1.-Map of the study area showing the spawn- ing aggregation site for razorback suckers in the middle Green River, Utah (upper Colorado River basin) at river kilometer (rkm) 504. channel, where the river moves around a large is- land (Figure 1). Razorback suckers congregate an- nually along a cobble-gravel bar at the initiation of spring flood flows (Tyus and Karp 1990; Modde and Irving 1998). Collection of razorback suckers.-Razorback suckers were captured by electrofishing (Smith- Root GGP transducer mounted in a johnboat). Three to six passes were made over the spawning bar weekly from 1 to 22 May 2000. Each fish captured was examined for a passive integrated transponder (PIT) tag and gender (i.e., presence of tubercles, expressing milt or eggs) and weighed (0.1 g) and measured (TL; mm). Fish without a PIT tag were tagged, and records were consulted to determine the origin of fish with PIT tags (i.e., wild or hatchery produced). As part of an inde- pendent recovery effort to develop a genetic re- fugia and broodstock for future stocking (i.e., Up- per Colorado River Basin Endangered Fishes Re- covery Program), all wild females and a limited number of wild males were removed from the river and transported to Ouray National Fish Hatchery (NFH). Attachment of radio transmitters.-Radio trans- mitters were externally attached to razorback suck- ers collected from the spawning area (as per Muell- er and Marsh 1998; Mueller et al. 2003). We used coded transmitters with a 149-Mhz frequency and a 44-d life span, weighing approximately 6.5 g (Lotek Engineering Inc.). Each transmitter was at- tached to the keel (anterior of the dorsal fin) on the dorsal surface of the fish. Before transmitter attachment, each fis methanesulfonate were placed in a s, 33 cm), and the gil solution of MS-22, the keel of each fis 0.23-cm bit. The d approximately 3.5 ment suture (Ethic( gauge,needle until i end. The transmitte (two anterior and tightly to the keel. wound following ; the fish was placed approximately 10 spawning site. Data-logging stagy was operated on an area (Figure 1). The antennas with four faced upstream, the the third pointed dii tennas were connec logging receiver. A a photovoltaic pane. tionary logger reco 6 June 2000. The re transmitter frequent tagged fish was det cy, code, time, and Signal strength all tional movement. F to determine when r approached and de well as the period e area. For the purpc nocturnal use of tl hours were (onside 0659 were consider Ground survey to cific locations of rac bar by monitoring i h periods in May: 1 25. Hourly location, determined (by tria riod. A single Lotel element Yagi antem two of five local be estimated by triang mark locations. Be global positioning s the island adjacent i were measured usii